This invention is concerned with dialysis probes, and relates in particular to a novel form of carrier for use as part of such a probe, and to a probe when using such a carrier.
Dialysis is the process of separating a liquid that is a solution in some solvent of one or more dissolved substance, or solute, mixed with one or more colloid (a material which is insoluble in the solvent and yet is present as particles which are so small that they behave in some ways as though they were in fact dissolved). In this process the mixture is placed in contact with a semipermeable membranexe2x80x94a solid barrier that acts as an extremely fine sievexe2x80x94through which the smaller solute particles can pass (diffuse) from one side to the other while the much larger colloidal particles cannot, and this diffusion/passage is then allowed/encouraged to take place. It is usual to have more solventxe2x80x94the perfusion fluidxe2x80x94running past on the other side of the membrane, so that the solute particles are washed away as they emerge. Such a dialysis system can be used to separate off and retain either of the two types of component. Thus, it may be that the colloidal material kept on the one side of the membrane is wanted, and the solute passing through to the other side of the membrane is not, or vice versa.
A well-known use of dialysis in the modern world is in the artificial kidney, or xe2x80x9cdialysis machinexe2x80x9d, where the mixture to be separated is the blood of a person with damaged or failed kidneys. This blood contains not only the desirable red blood cells as a colloidal solution but also an excess of potentially harmful dissolved materials that should normally have been removed by the Patient""s kidneys. In the dialysis treatment the Patient""s blood is continuously drawn out through a needle inserted into a vein (usually in the arm), and fed to the dialysis machine where the harmful constituents are separated off using a semipermeable membrane, as described above, and then returned, cleansed and xe2x80x9cpurifiedxe2x80x9d, into the Patient.
Another common, but not so well-known, use of dialysis is in the taking for subsequent chemical and biological analysis of tiny samples of body fluid/tissue components in human or veterinary medicine (in certain branches of modern Research Medicine much attention is being given to using this technique to assist in a determination of brain functions). Sampling is normally effected by inserting into the body a very fine, hollow probe containing a suitable membrane contactable with the body fluid or tissue, and pumping perfusion liquid therethrough to fetch out the diffused solute thereinxe2x80x94the material of interest. The body fluid to be sampled is usually, but not always, blood, and in such a case it is normal to insert the dialysis probe directly into an artery or vein, and allow the dialysis to occur in situ.
Dialysis probes can take a number of different physical forms. An earlier type of probe was essentially a sleeve-like tube a few millimeters in diameter and made of some impermeable material with one endxe2x80x94its distal (or xe2x80x9cfarxe2x80x9d) end, to be inserted into the bodyxe2x80x94closed by a suitable semipermeable membrane, and with smaller tubes sealingly inserted into the other endxe2x80x94the proximal (or xe2x80x9cnearxe2x80x9d) end, by which the tube was handledxe2x80x94to allow perfusion fluid to be supplied toxe2x80x94fed to and withdrawn from the interior (the lumen) ofxe2x80x94the sleeve. In use the distal end of such a probe is inserted into a suitable body tissue or cavityxe2x80x94some part of the brain, say, or a vein or arteryxe2x80x94and perfusion fluid is pumped in, through and out of the sleeve, taking with it any materials that have diffused from the body through the distal-end membrane into the sleeve""s lumen.
A more recent design of probe is essentially a sleeve-like tube itself made of semipermeable materialxe2x80x94and so forming the membranexe2x80x94blocked off at the distal end and with perfusion fluid supply tubes sealingly inserted into the proximal end. In use the membrane sleeve is inserted into the body, often through a previously-emplaced protective cannula (a slightly larger-diameter and mechanically-stronger sleeve, or sheath, positioned in the body to lead into the area of interest), and perfusion fluid is pumped in, through and out, taking with it any materials that have diffused from the body contents through the membrane walls of the sleeve into the lumen thereof.
Although all these forms of dialysis probe can provide excellent results, nevertheless they suffer from a number of significant drawbacks. For example, the membrane, which is extremely fragile, can too easily be damaged by the internalizationxe2x80x94the emplacement therewithinxe2x80x94of the perfusion liquid supply tubes. Moreover, fluid outflow (leakage) can too easily occur, so lessening the effectiveness of the device, due to the generation of back-pressure caused by the reduction of tubing diameter between the lumen of the membrane and the lumen of the internalized outlet tubing. In addition, such probes are difficult to insert into tissue because of the lack of rigidity of the body of the probe (the rigidity that exists is due solely to the internalized tubing, and this is often insufficient to prevent concertinaing or folding of the membrane when the device is inserted into tissue).
The present invention suggests a solution to - or at least a mitigation ofxe2x80x94these problems, thus providing a dialysis probe that can be readily and safely inserted into tissue as well as being relatively easy to manufacture, by a simple but surprising novel design of probe that incorporates a new sort of membrane carrier, or support. More specifically, the invention suggests the use of a mechanically-strong membrane carrier, or support, which is an elongate, rod-like, support member having at its distal end an eye, or a notch, through which a relatively-flexible, open-ended, tubular semipermeable membrane can be passed (rather like a strand of cotton is threaded through the eye of a needle), and wherein most preferably the opposed sides of the support member are shaped so as at least partially to accommodate the tubular membrane when the latter is folded back (at the eye/notch), U-fashion, and caused to lie against and either side of the support member between its distal and proximal ends. In use the tubular-membrane-carrying support member is inserted into the target area of the body, preferably through a previously-emplaced protective cannula, and perfusion fluid is pumped directly through the tubular membrane from one end to the other, taking with it any materials that have diffused from the body contents through the membrane walls into its lumen. It will be appreciated that the support member provides the probe with all the required mechanical strength, and that its simplified construction renders much easier its manufacture.
The present invention provides a dialysis probe comprising a membrane carrier; a relatively flexible, open-ended, semipermeable membrane; and inlet and outlet tubes, wherein the membrane carrier is a stiff, elongate support member having
two opposed sides and a proximal end and a distal end, the distal end having at least one eye or one notch through which the membrane passes and is folded, U-fashion, whereby the membrane lies along the two opposed sides of the support member and whereby the ends of the membrane are adjacent the proximal end of the support member; and
wherein the inlet and outlet tubes are sealingly joined to the two ends of the membrane, whereby perfusion liquid may be passed through the membrane.
The opposed sides of the support member may be shaped so as to accommodate at least partially the tubular membrane when the latter is so folded back and caused to lie against the support member. The invention provides a membrane carrier for use as part of a dialysis probe. In general, therefore, the carrier will be of dimensions and materials that are suitable for this use, and more is said about this hereinafter.